Preheat a grill with a cast iron skillet and caramelize the sliced onions in butter until deeply golden, then pull them off.
Flatten out the skirt steak and layer on the Swiss cheese and caramelized onions. Roll it up into a log.
Tie the log with two lengths of butcher's twine, then slice between the ties to make pinwheels. Season with salt, pepper and garlic.
Sear the pinwheels over high heat, then move to a cooler side of the grill and cook to about 125°F internal. Pull off and let rest.
Make the cheese crust: combine grated Gruyère, panko, melted butter and Parmesan. Pile it on top of each pinwheel and melt/torch it over the top before serving.
NOTE: Method transcribed from the video (rough) — quantities aren't given, so season and eyeball to taste. From Derek Wolf on Instagram.
